The server tries to send only the data that is needed. the server keeps calculating the range of each player so it can figure out what data is needed, other data is simply not send (because the player will never see a monster that is not on his/her screen.
How to find a players range? Using 62x32 isometric tiles
Used by server to find out what a player can see , and what info the server needs to send the player (non visible data doenst need to be send to player)
translated to 2D it will look like this : (translation rules : rotate 45 degree , height x 2)
With the 2d map its more easy to find the range of the player Lets say the red square is position 50,50, the maximum range is 10 squares, thats what the player can see. Its smart to expand the range with 2 more square so every client receives data earlier, in case of lags the player wont see too many jumping / or players appearing from nowhere
Monsters or players in the range of the player it will result in 'true' that way the server knows that it need to send this monster or player data to the player. The range is 11 tiles, which is exact the range that every player can 'see' on his/her screen.